"No, sir. It was my own apparatus I was using," explained Jack.

"I'll be more careful next time. I'll not put in so much of the chemical."

"I don't believe there had better be a 'next time' right away,"

declared Mr. Lenton.

"The next attempt you make to invent a powerful gas, you had better generate it in something stronger than a gla.s.s test tube.

Use an iron retort."

"Yes, sir," replied Jack.

"And now you had better report for your geometry lesson," went on the professor. "I need the laboratory now for a cla.s.s in physics. Just tell the janitor to come here and sweep up the broken gla.s.s. I am very glad neither of you boys was seriously injured. You must be more careful next time."

"Oh, Mark was careful enough," said Jack. "It was all my fault.

I didn't think the gas was quite so powerful."

"All right," answered the professor with a smile as Jack and Mark pa.s.sed out on their way to another cla.s.sroom.

The two lads, whom some of my readers have met before in the previous books of this series, were friends who had become acquainted under peculiar circ.u.mstances. They were orphans, and, after having had many trying experiences, each of them had left his cruel employers, and, unknown to each other previously, had met in a certain village, where they were obliged to beg for food. They decided to cast their lots together, and, boarding a freight train, started West.

The train, as told in the first volume to this series, called "Through the Air to the North Pole," was wrecked near a place where a certain Professor Amos Henderson, and his colored helper, Washington White, lived. Mr. Henderson was a learned scientist who was constantly building new wonderful machines. He was working on an airship, in which to set out and locate the North Pole, when he discovered Jack and Mark, injured in the freight wreck. He and Washington White carried the lads to the inventor's workshop, and there the boys recovered. When they were well enough, the professor invited them to live with him, and, more than that, to take a trip with him North Pole.

They went, in company with Washington and an old hunter, named Andy Sudds, and some other men, whom the professor took along to help him.

Many adventures befell the party. They had battles with wild beasts in the far north, and were attacked by savage Esquimaux.

Once they were caught in a terrible storm. They actually pa.s.sed over the exact location of the North Pole, and Professor Henderson made some interesting scientific observations.

In the second volume of this series, ent.i.tled "Under the Ocean to the South Pole," Professor Henderson, Jack, Mark, Washington and old Andy Sudds, made even a more remarkable trip. The professor had a theory that there was an open sea at the South Pole, and he wanted to prove it. He decided that the best way to get there was to go under the ocean in a submarine boat, and he and the boys built a very fine, craft, called the Porpoise, which was capable of being propelled under water at a great depth.

The voyagers had rather a hard time of it. They were caught in a great sea of Sarga.s.so gra.s.s, monstrous suckers held the boat in immense arms, and it required hard fighting to get free. The boys and the others had the novel experience of walking about on the bottom of the sea in new kinds of diving suits invented by the professor.

On their journey to the South Pole, the adventurers came upon a strange island in the Atlantic, far from the coast of South America. On it was a great whirlpool, into which the Porpoise was nearly sucked by a powerful current. They managed to escape, and had a glimpse of unfathomable depths. They pa.s.sed on, but could not forget the strange hole in the island.

Mark suggested that it might lead to the center of the earth, which is hollow, according to some scientists, and after some consideration, Professor Henderson, on his return from the South Pole, decided to go down the immense shaft.

To do this required a different kind of vessel from any he had yet built. He would need one that could sail on the water, and yet float in the air like a balloon or aeroplane.

How he built this queer craft and took a most remarkable voyage, you will find set down in the third book of this series, ent.i.tled "Five Thousand Miles Underground."

In their new craft, called the Flying Mermaid, the professor, the boys, Washington and Andy, sailed until they came to the great shaft leading downward. Then the ship rose in the air and descended through clouds of vapor. After many perils they reached the center of the earth, where they found a strange race of beings.

One day, to their horror, an earthquake dosed the shaft by which they had come to the center of the earth. The boys were in despair of ever getting to the surface again, but the professor had been prepared for this emergency, and he had built a strong cylinder, into which all the travelers placed themselves. Then it was projected into a powerful upward shooting column of water, which Professor Henderson hoped would take them to the surface of the earth. Nor was he mistaken. They had a terrible journey, but came safely out of it.

They opened the cylinder, to find themselves floating on the sea, and they were rescued by a pa.s.sing vessel. Of course, they had abandoned the Mermaid, leaving the craft in the center of the earth, but they had brought back with them some valuable diamonds, which formed their fortune.

This ended, for a time, the experiments of the professor, who decided to settle down to a quiet life, and write out the observations he had made on the three voyages. The boys wanted to get an education, and, investing their share from the sale of the diamonds, they took up a course at the Universal Electrical and Chemical College. Each had an ambition to become as great an inventor as was Professor Henderson, with whom they continued to live in a small city on the Maine coast. Washington White and Andy Sudds also dwelt with the professor, Andy going off on occasional hunting trips, and Washington acting as a sort of body servant to Mr. Henderson.

Jack and Mark had completed one term at the college, and were in the midst of the second when this story opens.

They had not lost their love for making queer voyages, and one of their greatest desires was to help the professor turn out a craft even more wonderful than the Electric Monarch, the Porpoise or the Flying Mermaid. It was in this connection that Jack was experimenting on the new gas, when the slight accident happened.

"Are you going to try that again?" asked Mark, as he and his chum walked along to their geometry cla.s.s.

"Sure," replied Jack. "I want that to succeed. I know I am on the right track."

"You came near getting blown off the track," remarked his companion, which was as near to a joke as he ever would come, for, though Jack was jolly and full of fun, Mark was more serious, inclined to take a sterner view of life.

"Oh, I'll succeed yet!" exclaimed Jack. "And when I do--you'll see something--that's all."

"And feel it, too," added Mark, putting his hand on his head, the book having raised quite a lump.

It was several days after this before the boys had the chance to work alone in the laboratory again, and Jack had to promise not to try his experiment with the new gas before this privilege was granted him.

"Want any help?" asked d.i.c.k Jenfer, another student, as he saw Jack and Mark enter the laboratory.

"Yes, if you want to hold a test tube for me," answered Jack.

"I'm going to try a new way of making oxygen."

"No, thanks! Not for mine!" exclaimed d.i.c.k as he turned away.

"I don't want to be around when you try your new experiments.

The old way of making oxygen is good enough for me."

"Well, I have a new scheme," went on Jack.

Soon he and Mark, whom he had again induced to help him, were busy with test tubes, rubber hose, Bunsen flames, jars of water, and all that is required to make oxygen.

Somewhat to his own surprise, the experiment Jack tried was a success. He collected a jarful of oxygen, generated in a way he had thought out for himself. It was much simpler than the usual method.

Just as he concluded the test, some one opened the laboratory door. It was Professor Lenton.

"I have a telegram for you," he said.

"A telegram?"

"Yes. It just arrived."

Jack tore open the yellow envelope.

"It's from Professor Henderson," he said.

"Is anything the matter?" asked Mark.

"I don't know," answered Jack. "It says: 'Come home at once.'

I wonder what's wrong?"

"I hope nothing serious," said Professor Lenton.

"You may both prepare to leave this afternoon. I am sorry. Let me hear from you when you reach Professor Henderson. I trust nothing has happened to him. He is too great a scientist for us to lose."